Short cylindrical specimens of Armco iron were tested at room temperature under compressive, axial loads at strains up to 0·6% and strain rates up to 103 in./in. sec. During loading, the axial stress was measured with a thin piezoelectric disk inserted between the specimen and the loading bar. The surface strain was measured with conventional epoxy-backed, foil strain gages, and the strain rate deduced by differentiating the strain-time data record. The stress, strain and strain rate data were plotted and were found to be approximated by a particular constitutive functional. The constitutive equation was then used along with the governing equations of motion and continuity in finding a numerical solution to the problem of a onedimensional plastic wave propagating in a rate sensitive bar caused by an initial axial stress σ(0, t). The numerical solutions for both stress and strain were found to agree favorably with the stress and strains which were measured, with embedded piezoelectric disks and strain gages, respectively, at two locations along a long iron bar wave propagation test. Thus, a constitutive relationship found to approximate the stress-strain-strain rate data generated in a short specimen impact test can be used to predict, with reasonably good agreement, the stresses and the strains measured in a long bar propagation test. This agreement indicates that the approximate constitutive function is a valid description of the flow properties of the material for the ranges of strain and strain rate observed.